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    <script>
        var a = 7;
        var num = 0;
        for ( var i = 1; i <= a; i++){
            if(a/i == 0){
                num++;
            }
        }
        if (num == 2 ){
            console.log('是质数');
        }else{
            console.log('不是质数');
        }
    </script>
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